The need of evidence-based management: the case of the of the Lesser White-Fronted Goose in Northern Norway

Abstract

In the face of global change, conservation actions are implemented worldwide to reduce the risk of extinction of declining populations. Population dynamics can be, however, the result of complex biotic and abiotic interactions. Therefore, it is often unsure to what extent management contributes to the recovery of a population if a proper scientific assessment is lacking. If conservation is the goal, it is crucial to quantify the impact of management actions. The Fennoscandian population of the Lesser White-Fronted Goose Anser erythropus (henceforth LWFG) experienced a dramatic decline in the last decades, to the point that conservation actions were deemed necessary. Among several conservation initiatives, culling of invasive red fox has become relevant, as red fox is perceived to be the main factor affecting reproductive success through predation on chicks and eggs. The LWFG population trend has reversed from negative to positive since the onset of the fox control program, suggesting an overall positive effect of management. However, in Arctic ecosystems, factors such cyclic small rodent populations and fluctuations in ungulate carrion availability can determine strong variation in annual predation pressure and in turn affect geese recruitment and survival. Using 19 years of data, we investigated to what extent red fox culling contributed to the recovery of the population. Specifically, we evaluated whether fox removal had the expected positive effect on LWFG reproductive success, while taking into account those factors outlined above that may confound the effect of the management action. We predicted LWFG breeding success to fluctuate synchronously with the rodent cycle due to an apparent facilitation mechanism. We also expect that increased availability of reindeer carcasses sustain foxes during the harsh arctic winter and enhance their survival, especially in years with deep snow that makes small rodents less accessible. Thus, we predicted lower reproductive success in years with high carcass abundance, due to an apparent competition mechanism. Moreover, we used these relationships to assess the relative impact of fox culling program. We found a strong positive effect of rodent density on geese breeding success, as well as a negative effect of the yearly amount of reindeer carcasses. However, there was no evidence in the data for any positive effect of fox culling. These results are relevant for the conservation of the LWFG population. Overall, this study emphasize the importance of scientifically evaluating the effectiveness of management actions by taking into account all the potential confounding factors.